Antifreeze concentrates based on amides, and coolant compositions comprising them and intended for protecting magnesium and magnesium alloys

ABSTRACT

The invention relates to antifreeze concentrates which are based on alkylene glycols or derivatives thereof or on glycerin, containing 0.05 to 10 wt. % of one or more cathoxylic acid amides and/or sulfonic acid amides in relation to the total quantity of concentrate.

The present invention relates to novel antifreeze concentrates based oncarboxamides or sulfonamides. The present invention furthermore relatesto ready-to-use aqueous coolant compositions which comprise saidantifreeze concentrates. The present invention also relates to the useof these antifreeze concentrates for the preparation of aqueous coolantcompositions for magnesium-containing and/or aluminum-containinginternal combustion engines.

Antifreeze concentrates for the cooling circulations of internalcombustion engines, for example in automobiles, generally containalkylene glycols, especially ethylene glycol or propylene glycol, as themain component. For use in the cooling system, they are diluted withwater and, in addition to protection from freezing, are also supposed toensure good heat removal. Alkylene glycol water mixtures are howeververy corrosive at the operating temperatures of internal combustionengines. The various metals and their alloys which occur in the coolingsystem therefore have to be adequately protected from various types ofcorrosion, for example pitting, crevice corrosion, erosion orcavitation.

The prior art discloses a large number of individual chemical substancesfor use as corrosion inhibitors in such cooling systems with a widerange of different metals, such as steel, cast iron, copper, brass,aluminum and their alloys and solder metals, for example tin solder.When they are used for cooling the engines now predominantly used by theautomotive industry and comprising gray cast iron or cast aluminumalloys, the resulting radiator antifreezes fulfill the expectations ofthem with regard to corrosion prevention.

In automotive construction, attempts are currently being made to reducethe fuel consumption by reducing the weight of motor vehicles. Thus,attempts have been made, for example, to reduce the weight of engines byconstructing them partly or wholly of magnesium or magnesium alloys.

However, tests have shown that, owing to the higher chemical reactivityof magnesium, the radiator antifreezes on the market today providevirtually no corrosion prevention for this metal and its alloys.

Nevertheless, there have been to date only a few patent publicationswhich offer solutions to these problems.

As long ago as 1931, DRP 569 771 (1) described a cooling liquid forinternal combustion engine parts consisting of magnesium alloys, whichliquid comprised a polyhydric alcohol containing small amounts of analkali metal fluoride, in the presence or absence of water.

In the same year, DRP 579 185 (2) described the use of alkali metalsulfides for the same purpose.

However, the use of fluorides or sulfides is no longer desirable todayowing to the toxicological hazards of these classes of substances.

WO 95/07323 (3) describes anhydrous radiator antifreezes based onmonopropylene glycol, containing molybdate, nitrate and an azolederivative, such as tolutriazole, preventing corrosion of variousmetals, including magnesium and magnesium alloys. However, anhydrousradiator antifreezes are not relevant in practice owing to their poorthermal conductivity.

EP 229 440 B1 (4) describes cooling concentrates which are also said tohave corrosion prevention properties for magnesium, containing aliphaticmonocarboxylic acid salts, aliphatic dicarboxylic acid salts and ahydrocarbon-triazole and, if required, additionally an alkali metalborate, silicate, benzoate, nitrate, nitrite or molybdate and/or ahydrocarbon-carbazole. However, specific corrosion test results are notdescribed for magnesium.

EP 251 480 B1 (5) describes coolant concentrates containing alkylbenzoicacid salts, aliphatic monocarboxylic acid salts and a triazole and, ifrequired, further components, which are said to lead to improvedcorrosion prevention not only in the case of the metals conventionallyused to date in engine construction but also in the case of magnesium.Here too, however, specific corrosion test results are not described formagnesium. As an improvement compared with (5) WO 00/22189 (6) describescooling liquids which contain a combination of carboxylic acid saltswith fluoride and/or fluorocarboxylic acid salts. However, adisadvantage here is in particular the use of the toxicologically unsafehydrochloric acid for the preparation of these compositions.

WO 99/19418 (7) describes a cooling liquid based on polyhydric alcoholsfor magnesium components, consisting of a combination of branchedaliphatic carboxylic acid salts and alkanolamine phosphates andtolutriazole/benzotriazole, to which, if required, further additives,such as aliphatic or aromatic mono- and/or dicarboxylic acid salts,mercaptobenzothiazole or carboxymethylcellulose, may be added. However,the corrosion test results are inadequate, in particular in the presenceof relatively large amounts of water.

It is an object of the present invention to provide correspondingantifreeze concentrates which no longer have the disadvantages of theprior art.

Little is known to date about the use of carboxamides or sulfonamides ascorrosion inhibitors. Thus, EP 320 281 A1 (8) describes the use ofanthranilamide in synthetic ester-based lubricating oils as a corrosioninhibitor for turbo engines.

EP 341 536 B1 (9) discloses the use of specific aromaticsulfonamidocarboxylic acids as water-soluble corrosion inhibitors forcleaning processes, cooling water, cooling lubricants, hydraulic fluidsand other functional solutions and emulsions. Corrosion of iron,aluminum, zinc, copper and their alloys is thereby suppressed.

The use of the amides as corrosion inhibitors in antifreeze concentratesbased on alkylene glycols, glycerol or their derivatives is unknown todate.

Surprisingly, it has now been found that carboxamides and sulfonamidesare effective corrosion inhibitors for magnesium and magnesium alloys inradiator antifreezes based on such antifreeze concentrates.

We have found that this object is achieved by antifreeze concentratesbased on alkylene glycols, glycerol or their derivatives, which contain

-   a) from 0.05 to 10% by weight, based on the total amount of the    concentrate, of one or more carboxamides and/or sulfonamides.

In a preferred embodiment, the component a) is formed from one or morealiphatic, cycloaliphatic, aromatic or heteroaromatic carboxamidesand/or sulfonamides, each of 2 to 16, preferably each of 3 to 12, carbonatoms.

The amides may be unsubstituted or alkyl-substituted on the nitrogenatom of the amido group, for example by C₁-C₄-alkyl. Aromatic orheteroaromatic skeletons of the molecule can of course also be alkylgroups. One or more, preferably one or two, amido groups may be presentin the molecule. The amides may additionally carry functional groups,preferably C₁-C₄-alkoxy, amino, chlorine, fluorine, hydroxyl and/oracetyl; in particular, such functional groups are present assubstituents on aromatic or heteroaromatic rings present.

Typical examples of such carboxamides and sulfonamides are stated below.

-   -   aromatic carboxamides:        -   benzamide        -   2-methylbenzamide        -   3-methylbenzamide        -   4-methylbenzamide        -   2,4-dimethylbenzamide        -   4-tert-butylbenzamide        -   3-methoxybenzamide        -   4-methoxybenzamide        -   2-aminobenzamide (anthranilamide)        -   3-aminobenzamide        -   4-aminobenzamide        -   3-amino-4-methylbenzamide        -   2-chlorobenzamide        -   3-chlorobenzamide        -   4-chlorobenzamide        -   2-fluorobenzamide        -   3-fluorobenzamide        -   4-fluorobenzamide        -   2,6-difluorobenzamide        -   4-hydroxybenzamide        -   2-hydroxybenzamide (salicylamide)        -   phthalamide        -   terephthalamide    -   heteroaromatic carboxamides:        -   nicotinamide (pyridine-3-carboxamide)        -   picolinamide (pyridine-2-carboxamide)    -   aliphatic carboxamides:        -   succinamide        -   adipamide        -   propionamide        -   hexanamide    -   cycloaliphatic carboxamides having the amido group as part of        the ring:        -   2-pyrrolidone        -   N-methyl-2-pyrrolidone        -   2-piperidone        -   ε-caprolactam    -   aromatic sulfonamides:        -   benzenesulfonamide        -   o-toluenesulfonamide        -   m-toluenesulfonamide        -   p-toluenesulfonamide        -   4-tert-butylbenzenesulfonamide        -   4-fluorobenzenesulfonamide        -   4-hydroxybenzenesulfonamide        -   2-aminobenzenesulfonamide        -   3-aminobenzenesulfonamide        -   4-aminobenzenesulfonamide        -   4-acetylbenzenesulfonamide

In a further preferred embodiment, the novel antifreeze concentratesadditionally contain nonionic compounds mentioned below

-   b) from 0.05 to 5% by weight, based on the total amount of the    concentrate, of one or more aliphatic, cycloaliphatic or aromatic    amines of 2 to 15 carbon atoms which may additionally contain ether    oxygen atoms or hydroxyl groups, and/or-   c) from 0.05 to 5% by weight, based on the total amount of the    concentrate, of one or more mononuclear or dinuclear unsaturated or    partly unsaturated heterocycles of 4 to 10 carbon atoms which may be    benzofused and may carry additional functional groups, and/or-   d) from 0.05 to 5% by weight of one or more    tetra-(C₁-C₈-alkoxy)silanes (tetra-C₁-C₈-alkyl esters of    orthosilicic acid), based on the total amount of concentrate.

Examples of suitable aliphatic, cycloaliphatic or aromatic amines b) of2 to 15, preferably 4 to 8, carbon atoms, which may additionally containether oxygen atoms or hydroxyl groups, are ethylamine, propylamine,isopropylamine, n-butylamine, isobutylamine, sec-butylamine,tert-butylamine, n-pentylamine, n-hexylamine, n-heptylamine,n-octylamine, isononylamine, di-n-propylamine, diisopropylamine,di-n-butylamine, mono-, di- and triethanolamine, piperidine, morpholine,aniline and benzylamine. Aliphatic and cycloaliphatic amines b) are as arule saturated.

The heterocycles c) are, for example, mononuclear five- or six-memberedsystems which have 1, 2 or 3 nitrogen atoms or have one nitrogen atomand one sulfur atom which may be benzofused. Dinuclear systemscomprising five- and/or six-membered ring moieties having typically 2,3, or 4 nitrogen atoms may also be used. The heterocycles c) mayadditionally carry functional groups, preferably C₁-C₄-alkoxy, aminoand/or mercapto. The heterocyclic skeleton can of course also carryalkyl groups.

Typical examples of heterocycles c) are benzotriazole, tolutriazole,hydrogenated tolutriazole, 1H-1,2,4-triazole, benzimidazole,benzothiazole, adenine, purine, 6-methoxypurine, indole, isoindole,isoindoline, pyridine, pyrimidine, 3,4-diaminopyridine,2-aminopyrimidine and 2-mercaptopyrimidine.

For example, tetramethoxysilane, tetraethoxysilane,tetra-n-propoxysilane or tetra-n-butoxysilane is suitable for thetetra-(C₁-C₈-alkoxy) silanes d).

Furthermore, the novel antifreeze concentrates may additionally containone or more of the compounds stated below

-   e) from 0.05 to 5% by weight, based on the total amount of the    concentrate, of one or more aliphatic or aromatic monocarboxylic    acids, each of 3 to 16 carbon atoms, in the form of their alkali    metal, ammonium or substituted ammonium salts and/or-   f) from 0.05 to 5% by weight, based on the total amount of    concentrate, of one or more aliphatic or aromatic dicarboxylic    acids, each of 4 to 20 carbon atoms, in the form of their alkali    metal, ammonium or substituted ammonium salts and/or-   g) one or more alkali metal borates, alkali metal phosphates, alkali    metal silicates, alkali metal nitrites, alkali metal or alkaline    earth metal nitrates, molybdates or alkali metal or alkaline earth    metal fluorides in amounts of, in each case, up to 1% by weight,    based on the total amount of the concentrate, and/or-   h) up to 1% by weight, based on the total amount of the concentrate,    of one or more hard water stabilizers based on polyacrylic acid,    polymaleic acid, acrylic acid/maleic acid copolymers,    polyvinylpyrrolidone, polyvinylimidazole,    vinylpyrrolidone/vinylimidazole copolymers and/or copolymers of    unsaturated carboxylic acids and olefins.

Compounds of groups e), f) and g) are additional corrosion inhibitors.

Examples of linear, branched or cyclic aliphatic monocarboxylic acids e)of these types are propionic acid, pentanoic acid, hexanoic acid,cyclohexylacetic acid, octanoic acid, 2-ethylhexanoic acid, nonanoicacid, isononanoic acid, decanoic acid, undecanoic acid and dodecanoicacid.

Particularly suitable aromatic monocarboxylic acid e) of this type isbenzoic acid, and, for example, C₁-to C₈-alkylbenzoic acids, such as o-,m-, p-methylbenzoic acid or p-tert-butylbenzoic acid, andhydroxyl-containing aromatic monocarboxylic acids, such as o-, m- orp-hydroxybenzoic acid or o-, m- or p-(hydroxymethyl)benzoic acid, orhalobenzoic acids, such as o-, m- or p-fluorobenzoic acid, are alsosuitable.

Typical examples of such dicarboxylic acids f) are malonic acid,succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid,azeleic acid, sebacic acid, undecanedioic acid, dodecanedioic acid,dicyclopentadienedicarboxylic acid, phthalic acid and terephthalic acid.

All stated carboxylic acids are present as alkali metal salts,especially as sodium or potassium salts, or as ammonium saltssubstituted ammonium salts (amine salts), for example withtrialkylamines or trialkanolamines.

Typical examples of additional corrosion inhibitors stated under g), aresodium tetrahydroborate (borax), disodium hydrogen phosphate, trisodiumphosphate, sodium metasilicate, sodium nitrite, sodium nitrate,magnesium nitrate, sodium fluoride, potassium fluoride, magnesiumfluoride and sodium molybdate.

When alkali metal silicates are present, they are expediently stabilizedby conventional organosilicophosphonates or organosilicosulfonates inconventional amounts.

In addition to said inhibitor components, for example, soluble magnesiumsalts of organic acids, e.g. magnesium benzenesulfonate, magnesiummethanesulfonate, magnesium acetate or magnesium propionate,hydrocarbazoles or quaternized imidazoles, as described in DE-A 196 05509, may also be used, in conventional amounts, as further inhibitors.

The pH of the novel antifreeze concentrates is usually from 4 to 11,preferably from 4 to 10, in particular from 4.5 to 8.5. The desired pHcan, if required, also be established by adding alkali metal hydroxide,ammonia or amines to the formulation, solid sodium hydroxide orpotassium hydroxide and aqueous sodium hydroxide or potassium hydroxidesolution being particularly suitable for this purpose. Carboxylic acidsto be concomitantly used are expediently added directly as correspondingalkali metal salts, in order to be automatically in the desired pHrange; however, the carboxylic acid may also be added as free acids andthen neutralized with alkali metal hydroxide, ammonia or amines and thedesired pH established.

Suitable liquid alcoholic freezing point depressants, which usuallyaccount of the main component (as a rule at least 75, in particular atleast 85, % by weight) of the novel antifreeze concentrates, arealkylene glycols and their derivatives and glycerol, in particularpropylene glycol and especially ethylene glycol. However, higher glycolsand glycol ethers are also suitable, for example diethylene glycol,dipropylene glycol and monoethers of glycols, such as the methyl, ethyl,propyl and butyl ethers of ethylene glycol, propylene glycol, diethyleneglycol and dipropylene glycol. Mixtures of such glycols and glycolethers and mixtures of these glycols with glycerol and, if required,with these glycol ethers may also be used.

In a preferred embodiment, the novel antifreeze concentrates are basedon ethylene glycol or propylene glycol or mixtures of alkylene glycolsor of glycerol with ethylene glycol or propylene glycol, which containin each case at least 95% by weight of ethylene glycol and/or propyleneglycol and/or glycerol.

The novel antifreeze concentrates may also contain conventional smallamounts of antifoam (as a rule amounts of from 0.003 to 0.008% byweight), dyes and bitter substances for reasons relating to hygiene andsafety in the case of swallowing (for example of the denatonium benzoatetype) as further conventional assistants.

The present invention also relates to ready-to-use aqueous coolantcompositions having a low freezing point, and in particular for radiatorprotection in the automotive sector, which comprise water and from 10 to90, in particular from 20 to 60, % by weight of the novel antifreezeconcentrates.

The novel antifreeze concentrates provide in particular more effectivecorrosion inhibition in the case of magnesium and magnesium alloys thanthe compositions of the prior art.

The examples which follow illustrate the invention without restrictingit.

EXAMPLES

The aqueous coolant compositions shown in Table 1 were prepared fromnovel antifreeze concentrates, it being possible to obtain theantifreeze concentrates, for example, simply be dissolving thecomponents in monoethylene glycol. The aqueous coolant compositions canbe prepared therefrom by simple dilution with water.

The testing of these aqueous coolant compositions is carried outdirectly without further dilution in the static hot surface test (ASTM D4340) using a magnesium test specimen of the alloy AZ91 HP or on a castaluminum test specimen of the alloy GAlSi6Cu4. Instead of concentratednitric acid, chromic acid, which is more suitable for this metal, wasused for cleaning the magnesium test specimen after the test.

The results are shown in Table 2. They show that, in the case ofmagnesium, substantially better corrosion prevention is achieved withthe novel coolant compositions than with compositions known from theprior art [potassium fluoride-containing formulation (Example 14);Glysantin® G 30 (commercial product from BASF Aktiengesellschaft, basedon conventional Organic Acid Technology)] and at the same time goodcorrosion prevention is present in the case of aluminum. Here, theincrease in weight in the case of aluminum in novel Example 11 indicatesthe formation of a stable protective layer.

TABLE 1 Novel aqueous coolant compositions Example Example ExampleExample Example Example Example Example Example Components [% by weight]1 2 3 4 5 6 7 8 9 Monoethylene glycol 69 69 69 69 69 69 69 69 69Adipamide 1 Benzamide 1 Anthranilamide 1 3-Aminobenzamide 14-Aminobenzamide 1 N-Methyl-2-pyrrolidone 1 Picolinamide 1 Nicotinamide1 Benzenesulfonamide 1 o-Toluenesulfonamide p-Toluenesulfonamide2-Aminobenzenesulfonamide Potassium fluoride TriethanolamineTolutriazole 1H-1,2,4-Triazole Salicylamide Distilled water 30 30 30 3030 30 30 30 30 Example Example Example Example 13 Example ExampleExample Example Components [% by weight] 10 11 12 (Comparison) 14 15 1617 Monoethylene glycol 69 69 69 69 69 69 69 69 Adipamide BenzamideAnthranilamide 3-Aminobenzamide 4-Aminobenzamide N-Methyl-2-pyrrolidonePicolinamide Nicotinamide Benzenesulfonamide o-Toluenesulfonamide 1p-Toluenesulfonamide 1 0.5 1 1 2-Aminobenzenesulfonamide 1 Potassiumfluoride 1 Triethanolamine 0.5 0.5 0.5 Tolutriazole 0.51H-1,2,4-Triazole 0.5 Salicylamide 1 Distilled water 30 30 30 30 30 3030 30

TABLE 2 Results in the static hot surface test according to ASTM D 4340Corrosion rate Example Example Example Example Example Example ExampleExample Example Example [mg/cm²/week] 1 2 3 4 5 6 7 8 9 10 Mg AZ91 HP−2.61 −4.52 −5.43 −2.14 −2.27 −3.87 −4.31 −3.02 −0.77 −2.37 GAlSi6Cu4 —−1.09 — — — — — — — — Glysantin ® G 30 Example (70% strength Corrosionrate Example Example 13 Example Example Example Example in H₂O)[mg/cm²/week] 11 12 (Comparison) 14 15 16 17 (Comparison) Mg AZ91 HP−1.97 −2.77 −12.42 −3.84 −0.66 −2.12 −3.00 −21.98 GAlSi6Cu4 +0.33 — — —+0.34 +0.29 — —

1. A process for protecting internal combustion engines comprisingmagnesium or magnesium alloys against corrosion, said process comprisingadding coolant compositions to cooling systems of the internalcombustion engines which comprise magnesium or magnesium alloys, whichcoolant compositions are based on an antifreeze concentrate which has apH of from 4 to 11, and is based on alkylene glycols or theirderivatives or on glycerol, containing a) from 0.05 to 10% by weight,based on the total amount of the concentrate, of one or morecarboxamides and/or sulfonamides and wherein when compound a) isaliphatic, amides of said compound a) are unsubstituted oralkyl-substituted on the nitrogen atom of the amido group.
 2. A processas claimed in claim 1, in which the component a) is formed from one ormore aliphatic, cycloaliphatic, aromatic, or heteroaromatic carboxamidesand/or sulfonamides, each of 2 to 16 carbon atoms.
 3. A process asclaimed in claim 1, in which the antifreeze concentrate additionallycontains nonionic compounds stated below, b) from 0.05 to 5% by weight,based on the total amount of the concentrate, of one or more aliphatic,cycloaliphatic or aromatic amines of 2 to 15 carbon atoms which mayadditionally contain either oxygen atoms or hydroxyl groups, and/or c)from 0.05 to 5% by weight, based on the total amount of the concentrate,of one or more mononuclear or dinuclear unsaturated or partlyunsaturated heterocycles of 4 to 10 carbon atoms which may be benzofusedand may carry additional functional groups, and/or d) from 0.05 to 5% byweight of one or more tetra-(C₁-C₈-alkoxy)silanes (tetra-C₁-C₈-alkylesters of orthosilicic acid), based on the total amount of concentrate.4. A process as claimed in claim 1, in which the antifreeze concentrateadditionally contains compounds stated below: e) from 0.05 to 5% byweight, based on the total amount of the concentrate, of one or morealiphatic, cycloaliphatic or aromatic monocarboxylic acids, each of 3 to16 carbon atoms, in the form of their alkali metal, ammonium orsubstituted ammonium salts and/or f) from 0.05 to 5% by weight, based onthe total amount of concentrate, of one or more aliphatic or aromaticdicarboxylic acids, each of 3 to 20 carbon atoms, in the form of theiralkali metal, ammonium or substituted ammonium salts and/or g) one ormore alkali metal borates, alkali metal phosphates, alkali metalsilicates, alkali metal nitrites, alkali metal or alkaline earth metalnitrates, molybdates or alkali metal or alkaline earth metal fluoridesin amounts of, in each case, up to 1% by weight, based on the totalamount of the concentrate, and/or h) up to 1% by weight, based on thetotal amount of the concentrate, of one or more hard water stabilizersbased on polyacrylic acid, polymaleic acid, acrylic acid/maleic acidcopolymers, polyvinylpyrrolidone, polyvinylimidazole,vinylpyrrolidone/vinylimidazole copolymers and/or copolymers ofunsaturated carboxylic acids and olefins.
 5. A process as claimed inclaim 1, in which the antifreeze concentrate is based on ethylene glycolor propylene glycol or a mixture of alkylene glycols or of glycerol withethylene glycol and propylene glycol, which contains in each case atleast 95% by weight of ethylene glycol and/or propylene glycol and/orglycerol.
 6. A process as claimed in claim 1, in which the coolantcomposition is a ready-to-use aqueous coolant composition having adepressed freezing point, which comprises water and from 10 to 90% byweight of an antifreeze concentrate as claimed in claim
 1. 7. A processas claimed in claim 1, in which the component a) is formed from one ormore aliphatic, cycloaliphatic, aromatic, or heteroaromatic carboxamidesand/or sulfonamides, each of 3 to 12 carbon atoms.
 8. In a process ofprotecting internal combustion engines containing magnesium or magnesiumalloys from corrosion and containing a coolant system, the improvementcomprising adding to the coolant system of said engine an antifreezeconcentrate, based on alkylene glycols or their derivates or onglycerol, containing a) from 0.05 to 10% by weight, based on the totalamount of the concentrate, of one or more carboxamides and/orsulfonamides.
 9. A process as claimed in claim 1, wherein when compounda) is aromatic or heteroaromatic, amides and/or rings of said compounda) are unsubstituted or substituted with one or more functional groupschosen from a group consisting of C₁-C₄-alkoxy, amino, chlorine,fluorine, hydroxyl, and acetyl.
 10. A process as claimed in claim 1,wherein the coolant composition comprises from 1 to 10% by weight ofcomponent a).
 11. A process as claimed in claim 1, wherein the componenta) is formed from one or more aliphatic carboxamides and/or one or morealiphatic sulfonamides.
 12. A process as claimed in claim 1, wherein thecomponent a) comprises one or more sulfonamides.
 13. A process asclaimed in claim 12, wherein the coolant composition comprises from 0.5to 10% by weight of component a).
 14. A process as claimed in claim 12,wherein the coolant composition comprises from 1 to 10% by weight ofcomponent a).
 15. A process as claimed in claim 12, wherein the one ormore sulfonamides is/are aliphatic.